Study for Exchange 2003 or Exchange 2007?

I have CBT Nuggets and Transcender for Exchange 2003.
With Exchange 2007 out is it worth putting my effort into the new one instead?
How much different is Exchange 2003 from Exchange 2007?
With Exchange 2007 out is it worth putting my effort into the new one instead?
How much different is Exchange 2003 from Exchange 2007?
Comments
If you're going to right away I'd study up on Exchange 2003, first, because if you're going to take over for a company that wants to upgrade to 2007, you're still going to have to maintain the 2003 environment for a while and there are some nuances that you need to understand. Before you do that, however, you must have the prerequisite understanding of DNS (be very fluent in the Windows specific DNS), be very comfortable with Active Directory, and have a good understanding of TCP/IP principles like basic subnetting.
Recent: 11/2019 - RHCSA (RHEL 7); 2/2019 - Updated VCP to 6.5 (just a few days before VMware discontinued the re-cert policy...)
Working on: RHCE/Ansible
Future: Probably continued Red Hat Immersion, Possibly VCAP Design, or maybe a completely different path. Depends on job demands...